Go to the shrine, when asked to insert CD, put Monster Rancher Hop A Bout
(PS)CD. You will get rare Zan (Zan/???) monster that looks Zan but on
handwriting style or Doodles style. Very unique and funny monster.

If you happen to accidentally get a monster you do not want (usually by pressing X too fast when regenerating monsters), you can get rid of it for good. When you go to the association and select "Retire", the lady will ask you if you want to freeze it. Tell her "No". She will then ask if you want to retire it. Tell her "Yes". It will not use up a spot in your freezer and you will get rid of an unwanted monster

Gamepro got there hands on this game and made a great monster.
It's name is Gameprobot and can be achieved by going to the shrine and
putting in Gameshark2v2(for PS2). It will come out a shiny metallic
dragon.

Pandora's Disk
There is a Pandora's Disk for this game and the best thing is you don't
need to buy it.This Pandora's Disk is built right into the game.When your
at the place to make monsters but instead of putting a game in just keep
the Monster Rancher 4 disk in and like the Pandra's Disk for Monster
Rancher 2 you will get a special monster depending on your breeder lvl.

To Unlock a Monkey from Ape Escape with the red pants, go to the shrine
one you can create monsters. When it asks for you to put in a disk, put in
the 1st Ape Escape game. You now have the monkey from Ape Escape with
the menacing Glare and red boxing gloves.

If you have a new monster that has trouble in adventures, use this trick to get it leveled up faster. Go to an adventure, it does not matter where. Make sure you have a powerful monster in your party. Battle an enemy, and instead of KOing them with the powerful monster, weaken them so that they only have a sliver of life renamining. Then, switch with your weaker monster and allow it to finish the monster. The experience will be rewarded mostly to the weaker monster. This is an easy way to give it experience and allow it to gain new attacks and abilities.

Successfully complete the game and save it once the credits are done. Then, reload your game. Two weeks after you completed the game, a feather from Suzaku is left behind. He asks you to train a Pheonix, and tells you that the feather allows you to revive a Phoenix from a disc. From this point on you can revive Phoenix monsters.

When you fill up the traits on your monster's data you can get rid of unwanted traits like Genius. To do so, level up until you get another trait. You will be asked if you want to delete a trait to make room for a new one.

A very easy way to go through the storyline quickly is to get a monster dedicated to Power and Accuracy, Train it in Power and Accuracy mostly, but have all its other stats at level 10. The power and accuracy easily raise to level 20 to 30. Most monsters through E, D, C, B, and A classes will not be able to dodge your attacks, and they will be KOed in one to two moves. This works well against Bosses and in dungeons, since they attack rarely which leaves them wide open for quick attacks that will do devastating damage. Having 700 Power and Accuracy makes the final Boss very easy to defeat in both forms. Note: Monsters such as Bleakons are perfect for this, since their Power and Accuracy are raised quickly and easily.

Successfully complete the game. Once done, wait three weeks. After the third week you will get a visit from Mr. Karnab. He informs you that new passageways have opened in the ruins that you have. Go to adventure and press Right or Left to switch from normal adventure to Adventure +. Adventure + is much harder then normal adventure. All the wild monsters are "S" rank, and the ruins have many levels (about 10). Of course, the items are much better in Adventure +.